1. Field of the Invention
The present invention relates to an image sensing apparatus incorporated with an image sensor having two or more different photoelectric conversion characteristics, as well as an image sensing method; and more particularly to an image sensing apparatus and an image sensing method that enable to control sensitivity with respect to image signals having different characteristics to be outputted from an image sensor.
2. Description of the Related Art
In recent years, in an image sensing apparatus such as a digital camera, as high-quality performance is demanded, a technology of expanding a luminance range i.e. a dynamic range of a subject image to be captured by an image sensor is required. In expanding the dynamic range, there is known an image sensor having different photoelectric conversion characteristics i.e. a linear characteristic that an electric signal is linearly converted with respect to an incident light amount and outputted, and a logarithmic characteristic that an electric signal is logarithmically converted with respect to an incident light amount and outputted. In the image sensor, an image signal having a linear characteristic is outputted in a low luminance range, and an image signal having a logarithmic characteristic is outputted in a high luminance range. Hereinafter, an image sensor having a linear characteristic and a logarithmic characteristic as photoelectric conversion characteristics is called a “linear-logarithmic sensor”.
Generally, in a so-called silver halide camera i.e. a film camera, ISO sensitivity correction is performed as one of various correcting operations to be performed with respect to a photographic image. In the case where sensitivity correction is performed in a digital camera, for instance, imaging sensitivity is increased, multiplication is performed with respect to an image signal having a linear characteristic, and summation is performed with respect to an image signal having a logarithmic characteristic (see e.g. Japanese Unexamined Patent Publication No. 2006-352804 (D1)). In the conventional art, as sensitivity is increased in an analog signal status, the dynamic range may be changed.